IBM Power Systems 9009-41A Manual page 83

Figure 67. Grasping the system backplane and lowering it into the chassis
b) Tilt the backplane so that the front end is high and the back end is low as you continue to lower
the backplane into the chassis. When the system backplane catches on the pins (A) on the power
supply cage, lower the front end enough so that it clears the pins. See the following image.
Removing and replacing the system backplane in the 9009-41A, 9009-42A, or 9223-42H 69